Authorities arrested four suspects on Wednesday over the 2002 murder of associate professor Necip Hablemitoğlu.

The Chief Prosecutor’s Office in the Turkish capital Ankara issued arrest warrants for nine people and a manhunt is underway to capture five other suspects. Among the wanted suspects is retired colonel M.L.G. M.L.G. is a former member of the Turkish Armed Forces (TSK) elite Special Forces Command and was arrested in 2009 in the notorious Ergenekon investigation. He was sentenced to 20 years in 2013 on charges of membership in a terrorist group but was released in 2014. The Ergenekon investigation is viewed as a plot by the Gülenist Terror Group (FETÖ) to imprison military officers opposing it and through its infiltrators in law enforcement and judiciary, FETÖ was accused of concocting sham trials for the Ergenekon "terrorist group."

Hablemitoğlu was shot dead outside his home two decades ago and was working on an expose on crimes of FETÖ, which back then posed as a charity movement with religious undertones, at the time of his murder.

Nuri Gökhan Bozkır, a suspect in Hablemitoğlu’s murder, was brought to Turkey from Ukraine earlier this year and was arrested in February on charges of membership in a terrorist group and manslaughter. Six suspects linked to Bozkır were detained in February and two were remanded into custody, while others were released.

Sabah newspaper had reported in February that authorities had evidence that shows Mustafa Özcan, a top figure of FETÖ, orchestrated the murder plot through its subordinates and coordinated it with a former member of the National Intelligence Organization (MIT) who was jailed last year for his ties to the group.

Hablemitoğlu was an outspoken figure on secret organizations in Turkey and activities of foreign foundations in the country before his murder. His book on FETÖ, named "Köstebek" ("Insider"), was published posthumously and is viewed as the first comprehensive nonfiction book on the terrorist group’s secret structure and its attempts to infiltrate the state. Media outlets have long reported suspicions over FETÖ’s role in the murder but the first proper investigation into the allegations was launched in 2016, the year the terrorist group attempted to stage a deadly coup.

Security sources quoted by Sabah newspaper say Mustafa Özcan is the prime suspect in the case along with Enver Altaylı, a former intelligence official convicted in a FETÖ-linked case last year. Evidence collected by the prosecutor’s office shows Özcan tried to meet Hablemitoğlu in 2002, before the latter’s death and Altaylı was instrumental in setting up a meeting, along with N.A., another suspect in the case identified only with his initials. It is unclear why Özcan attempted to reach out to Hablemitoğlu. The victim’s family had told police after the murder that Hablemitoğlu had received threatening phone calls and emails before the murder. Altaylı is also named as a "middleman" in the case of FETÖ’s attempt to recruit people from the Special Forces Command for an attempt to assassinate Hablemitoğlu.